Addressing obesity early in life is a significant public health opportunity. This study will be the first of its kind to assess the extent to which large-scle changes in nutrition policy could improve weight outcomes for children. Results from this study will help inform policymakers of the potential benefits of investing in improved diet quality for children. The school food environment may influence the dietary habits of children, and therefore, the risk of obesity. The National School Lunch Program (NSLP) is a key component of the school food environment, serving over 31 million children lunches daily. As directed by the Healthy, Hunger-Free Kids Act of 2010, the Department of Agriculture instituted new NSLP nutrition standards for lunches served to school children. The standards, implemented in the 2012-2013 school year, are designed to lead to improvements in meal quality and nutrition-related child outcomes. Key components of the standards include: increasing fruits and vegetables and whole grains offered, eliminating high fat dairy products, and limiting calories, sodium, and saturated fat. This research will address two specific aims: 1) To examine whether the new school nutrition standards have affected elementary school children's body mass index (BMI) and risk of obesity; and 2) To examine, in two specific contexts, whether or not school nutrition standards being implemented as intended and to document the obstacles schools faced in implementing the new school nutrition standards. This study will employ a mixed methods strategy to assess the impact of the new NSLP meal standards on child weight outcomes. A non-experimental design using secondary data and triple difference models will be used to estimate the impact of the new NSLP nutrition standards on child BMI and weight status. A two-level qualitative study composed of semi-structured key informant interviews and school lunch observation will provide descriptive evidence on the implementation of nutrition standards across school districts and on possible pathways through which nutritional standards may impact child weight.